The novel cloth-like fibrous laminate is useful as disposable toweling, bed pads, diaper liners, sanitary napkins, wipes, wound dressings, and filter materials which are capable of removing moisture from non-aqueous filtrates. In one of its referred embodiments, a composite fabric comprising a superabsorbent scrim layer sandwiched between layers of dry laid nonwoven cellulosic fibers is produced as a strong laminate structure of high liquid-absorbency which is soft to the touch.
Numerous proposals have been made for the manufacture of cellulosic composite products useful as disposable towels and similar products. Two desirable properties of such absorbent products, namely, high-liquid absorbency and superior wet strength are virtually antithetical. High absorbency is usually associated with a fibrous structure of high porosity but low tensile strength, whereas wet strength usually involves the use of binders or compacted fibers exhibiting relatively low absorbency.
A method for the manufacture of a cloth-like composite laminate is disclosed in U.S. Pat. No. 4,634,621 to Manning et al, in which scrim coated with a thermoplastic binder is inserted between two non-woven layers bonded with a latex adhesive and the composite heated to a temperature sufficient to activate the thermoplastic binder. A scrim reinforced, cloth-like composite laminate is produced having both excellent dry and wet strength properties.
A number of patents are directed to methods for incorporating superabsorbent materials, commonly referred to in the art as SAM's, into cellulosic composites to form products of greatly enhanced absorbency for liquids. For example, Korpman, U.S. Pat. No. 4,413,995 discloses an absorbent panel structure useful in various hygienic products in which a paper or fabric substrate is coated with a reactive composition of a liquid polyhydroxy organic compound and a particulate water-insoluble, water swellable absorbent polymer. Watt, in U.S. Pat. No. 4,600,462, discloses a latex bonded, air laid web of enhanced absorbency to which a water soluble hydrophile is added and dried on the web. An absorbent pad assembly in which a hydrophilic polymer coating is applied to one surface of one pad and covered with another pad adjacent the coated surface is disclosed in U.S. Pat. No. 4,461,621 to Karami et al.
In accordance with this invention, a strong disposable absorbent laminate of improved water absorbency is formed by incorporating a superabsorbent material on a polyester or fiberglass scrim and covering the scrim with a layer of cellulosic or synthetic fibers. In one specific embodiment of the invention, the scrim is coated with an adhesive, e.g. a polyvinyl alcohol latex, to which superabsorbent powder is added to form a coating on one or both sides of the scrim, and the thus formed superabsorbent scrim is covered with a web of cellulosic fibers. The resultant product is a strong laminate structure with superior water absorbency and a cloth-like appearance and feel.
In accordance with a preferred embodiment of this invention, a cloth-like composite laminate is formed which comprises two nonwoven layers of cellulosic fibers attached to the opposite sides of a scrim or screen which has been coated or impregnated with a superabsorbent hydrophilic polymer.
A number of superabsorbent polymers are known in the art. U.S. Pat. No. 4,600,458 to Kramer et al., for example, includes a long list of patents disclosing superabsorbent polymers useful in absorbent structures in which the superabsorbent polymers are incorporated into an absorbent fibrous web or laminate. Among the polymers disclosed for this purpose are saponified starch-polyacrylonitrile graft copolymers, crosslinked/grafted cellulose, saponified vinyl acetate-acrylic acid copolymers, starch grafted polyvinyl acetate, acrylic acid polymers, crosslinked polyethylene oxide, and the like. In the method of this patent, superabsorbent solid particles are layered between webs of fibrous material and the layered stacks of webs crimped to retain the solid absorbent in place. McFarland et al., U.S. Pat. No. 4,655,757 incorporates solid particles of superabsorbent material into a coformed layer of meltblown fibers containing wood fibers for improved absorbency. Among the superabsorbents mentioned therein are those formed from hydrolyzed cross-linked polyacrylamides, polyacrylates, polymers of acrylic polymers of their copolymers. Sodium polyacrylate hydrocolloid particles are preferred as superabsorbents.
Fibrous silvers and absorbent structures having superabsorbents or hydrocolloids distributed therethrough are disclosed in U.S. Pat. Nos. 4,340,556 to Ciencewicki and 4,596,567 to Iskra wherein some superabsorbents are described as having a backbone of natural or synthetic polymers with hydrophilic groups, or polymers containing hydrophilic groups, chemically bonded thereto or in intimate admixture therewith. Among the superabsorbents mentioned therein are modified natural and regenerated polymers, such as polysaccharides including cellulose, and starch and regenerated cellulose which are modified by being carboxylated, phosphonoalkylated, sulfoalkylated, or phosphorylated to render them highly hydrophilic. These polymers may be cross-linked to render them water insoluble, all as described in U.S. Pat. No. 4,105,033 to Chatterjee et al.
The superabsorbent polymer and cross linker may be any of those already known in the chemical literature as well as those resulting from continued research and development to produce water insoluble cross linked polymer products of enhanced hydrophilic propensity. Currently, superabsorbents suitable for application to the scrim used in the toweling of this invention include the metal ion crosslinked polymers described in U.S. Pat. No. 4,090,013 and a polyacrylate absorbent containing both amide and carboxylate groups prepared by radiation polymerization and crosslinking as described in U.S. Pat. No. 4,192,727. Hydrophilic polymers that are reacted with organic crosslinkers as described in the U.S. Pat. No. 4,310,593 are further examples of superabsorbents that may be applied to the scrim.
The scrim is formed of a continuous filament of nonwoven material such as rayon, nylon, polyester, polypropylene, aramids, and glass. A polyester scrim or screen sold under the trademark Bayex by Bay Mills, Ltd., of Canada is illustrative of a desirable reinforcement for production of the novel toweling of high wet strength and superior water absorbency. The scrim will in most cases have a mesh opening of 2 to 5 mm between fibers and will contribute a weight in the range of 0.2 to 2.0 ounces per square yard to the total weight of the multi-ply towel.
The two layers of nonwoven cellulosic fibers which are attached to the opposite sides of the superabsorbent coated scrim or screen may be produced by any of the many known procedures. For example, previously mentioned U.S. Pat. No. 4,634,621, incorporated herein by reference, discloses an operation in which dry fibers are laid on two separate belts and bonded with a latex adhesive forming two separate air laid bonded cellulosic webs which are then brought into contact with the opposite sides of a scrim coated with a thermoplastic resin. In the process of this patent, the scrim has a thermoplastic polymer binder applied as a coating to each of its two sides. The nonwoven cellulosic layers and the intermediate binder-coated scrim are finally passed through a heated lamination station to cause adhesion of the cellulosic layers to the scrim.
In accordance with a preferred embodiment of this invention, each of the cellulose webs which is brought into contact with the scrim is given a coating of binder on its surface nearest the scrim so that surface fibers of each nonwoven layer become attached on contact with the superabsorbent scrim and on curing of the binder, the cellulosic layers are bonded to the scrim to provide a unitary product of high wet strength and greatly enhanced absorbency.
Alternatively, it is in many cases preferable to bring the nonwoven cellulosic layers into contact with the scrim immediately after the hydrophilic polymer has been applied thereon. In such cases, the wet surface coating on the scrim contacts the cellulosic layers and during the drying or curing reaction creates a bonding of the cellulosic layers to the scrim.